
for \(1\le i \le n\)  where \(\tilde{h}_i\)  is the \(i\) -th row of \(H\) .
Unfortunately, since the regularizer penalises
every entry of \(A\) , the implementation of (REF ) costs \(\mathcal {O}(n^4)\)  operations
to compute the full model \(A\) .
Thus, we recommend pursuing inexact but efficient solutions, possibly using descent methods [1]}.
